Apeil 15, 1904.] 



SCIENCE. 



607 



Missouri except that the former carries the 

 greater quantity of water. 



The immediate effect of permanently 

 diminishing the volume of flow in the river 

 would be to impair its value for navigation. 

 This effect would follow quickly — within a 

 very few years. A later effect would be to 

 diminish the capacity of the channel to hold 

 the floods, and so raise the flood heights. 

 How rapidly this shrinkage would take 

 place can not be stated ; but it would begin 

 at once and go on until the relations of 

 volume and channel capacity found an ad- 

 justment in which the natural bank level 

 would approximate the mean annual flood 

 height. This would mean overflow in all 

 floods above the mean. 



The modus operandi of the filling up 

 process is simple enough. The flood leaves 

 high, vertical banks on the concave sides of 

 the bends. The enfeebled stream at low 

 water cuts into those banks at the base. 

 The undermined earth falls down in great 

 masses into the pool. The weak current is 

 unable to carry it away, and so climbs up 

 over it and goes on gnawing at the base 

 of the bank. By this process it grades 

 down the bank and \fills up the pool to 

 greater or less extent. This operation goes 

 on during every low water in the Missis- 

 sippi River now. Vast quantities of earth 

 are knocked down into the pools by the un- 

 dermining of the concave banks. But when 

 the flood follows it digs that material out 

 again and piles it up on the convex sides of 

 the bends. One of the striking sights to 

 be seen on going down the river at low 

 water after a great flood is the immense 

 bars piled high up above the low-water line 

 by the preceding flood. The present chan- 

 nel is the result of nature's adjustment 

 between this filling-up process and this 

 digging-out process. If the activity and 

 energy of the digging-out process were 

 diminished the channel would fill up until 

 the adjustment had been restored. 



If the present discharge down the main 

 stream were reduced by one half at all 

 stages, the energy of the excavating force 

 would be reduced out of all proportion to 

 the reduction of the effectiveness of the 

 filling-up force. The low-water current 

 would eat away the base of the high banks 

 and fill up the pools with material which 

 the diminished flood would be unable to 

 remove. The result would be at last a re- 

 adjustment of forces with shallower pools, 

 lower concave banks, less filling up, less 

 digging out, less everything that pertains 

 to the life of a river. Then when the great 

 flood came it would find a diminished chan- 

 nel to carry it aud would overflow the 

 country as before. There would be less 

 water to take care of and it may be that 

 the floods could be restrained by levees of 

 less height. As against that gain, however, 

 we would have another river to take care of 

 with its low water and high water, its bars, 

 floods, overflows, levees, creirasses and other 

 burdens and calamities. All in all, our last 

 state would be worse than our first. 



As for navigation, the present large 

 schemes for ten feet or more from Cairo 

 down would all go glimmering. The superb 

 advantages which nature gave us in the one 

 great river would be thrown away in ex- 

 change for two smaller rivers, more expen- 

 sive to control, more destructive and less 

 useful. 



I have been discussing the feasibility of 

 general protection of the alluvial valley 

 from overflow by outlets. I have en- 

 deavored to take a practical view of the 

 question by assuming definite plans with 

 outlets and auxiliary channels definitely 

 located. It seems to me that it is only 

 necessary to approach the question in this 

 direct and practical way to make it ap- 

 parent that the outlet theory is a dream 

 impossible of realization. 



It does not follow from this that there is 

 no situation in which no outlet of any kind 



